Indicator definition

The indicator shows the fraction of the urban population that is potentially exposed to ambient air (1) concentrations of pollutants (2) in excess of the EU limit value set for the protection of human health.

The urban population considered is the total number of people living in cities with at least one monitoring station.

Exceedance of air quality limit values occurs when the concentration of air pollutants exceeds the limit values specified in the first Daughter Directive of the Air Quality Framework Directive for SO2, PM10 (3), NO2 and the target values for O3 as specified in the third Daughter Directive. Where there are multiple limit values (see section on Policy Targets), the indicator uses the most stringent case:

Sulphur dioxide (SO2): the daily limit value;

Nitrogen dioxide (NO2): the annual limit value;

Particulate matter (PM10): the annual limit value;

Ozone (O3): the short term objective.

(1) "Ambient air" shall mean outdoor air in the troposphere, excluding work places.

(2) "pollutant" shall mean any substance introduced directly or indirectly by man into the ambient air and likely to have harmful effects on human health and/or the environment as a whole.

Units

Percentage of the urban population in Europe potentially exposed to ambient air concentrations (in mg/m3) of sulphur dioxide (SO2), particulate matter (PM10), nitrogen dioxide (NO2) and ozone (O3) in excess of the EU limit value set for the protection of human health.

Key policy question: What progress is being made in reducing concentrations of air pollutants in urban areas to below the limit values (for SO2, NO2 and PM10) or the target values (for ozone) defined in the air quality framework directive and its daughter directives?

Key messages

Particulate Matter (PM10)

In the period 1997-2002, 25-55% of the urban population was potentially exposed to ambient air concentrations of fine particulate matter (PM10) in excess of the EU limit value set for the protection of human health (50 microgramme/m3 daily mean not be exceeded more than 35 days a calendar year).

Nitrogen dioxide (NO2)

In the period 1996-2002, 25-50% of the urban population was potentially exposed to ambient air nitrogen dioxide (NO2) concentrations above the EU limit value set for the protection of human health (40 microgramme NO2/m3 annual mean).

No exceedances of the short-term limit value (200 microgramme NO2/m3 as an hourly value, not to be exceeded more than 18 times a calendar year) were observed.

Ozone (O3)

In the period 1996-2002, 20-30% of the urban population in Europe was exposed to ambient ozone concentrations exceeding the EU target value set for the protection of human health (120 microgramme O3/m3 daily maximum 8-hourly average, not to be exceeded more than 25 times a calendar year).

Sulphur dioxide (SO2)

In the period 1996-2002, the fraction of the urban population in EEA-31 that is potentially exposed to ambient air concentrations of sulphur dioxide in excess of the EU limit value set for the protection of human health (125 microgrammeSO2/m3 daily mean not to be exceeded more than three days a year), decreased to less than 1%, and as such the EU limit value set is close to being met.

Exceedance of air quality limit value of PM10 in urban areas (EEA member countries), 1996-2002

Note:For years before 1997 representative monitoring data is not available

Exceedance of air quality limit values of NO2 in urban areas (EEA member countries), 1996-2002

Note:Over the years 1996-2002 the total population, for which exposure estimates are made, increased from 56 to 111 million people due to an increasing number of monitoring stations reporting air quality data

Exceedance of air quality target values for ozone in urban areas (EEA member countries), 1996-2002

Note:Over the years 1996 - 2002 the total population for which exposure estimates are made, increases from 50 to 110 million people due to an increasing number of monitoring station reporting under the Exchange of Information Decision

Key assessment

Particulate Matter (PM10)

PM10 in the atmosphere can result from direct emissions (primary PM10) or emissions of particulate precursors (nitrogen oxides, sulphur dioxide, ammonia and organic compounds) which are partly transformed into particles by chemical reactions in the atmosphere (secondary PM10).

Monitoring of PM10 has only started recently and available data before 1997 is not representative for Europe. For the period 1997-2002, the number of monitoring stations was still relatively small and results may not be representative for all parts of Europe (Buijsman et al., 2004). Notwithstanding these limitations, it is clear that a significant proportion of the urban population (25-55%) was exposed to concentrations of particulate matter in excess of the EU limit values set for the protection of human health (Figure 1).

The observed time series is too short and the natural meteorological variability is too large to draw any firm conclusion on a possible trend in the data. Preliminary analyses indicate a downward change in the highest daily mean PM10 values although for the majority of stations the observed change is statistically not significant. In Figure 2, the 36th highest daily mean is shown; compliance with the short-term limit value is assured when this value is below 50 microgramme/m3.

Emissions of the gaseous precursors for secondary PM10 are being reduced by enforcement of EU legislation and UN-ECE CLRTAP protocols. Abatement techniques to reduce precursor emissions often also reduces the primary particulate emissions. Other measures (e.g. traffic measures from Auto-Oil-I and II, waste incineration directives) should further reduce PM10 emissions.

Despite the likely future reductions in emissions, concentrations of PM10 in most of the urban areas in the EEA are expected to remain well above the short-term limit values in the near future.

Nitrogen dioxide (NO2)

The main source of nitrogen oxides emissions to the air is the use of fuels; road transport, power plants and industrial boilers account for more than 95% of European emissions.

About 30% of the urban population lives in cities with urban background concentrations in excess of the 40 microgramme NO2/m3 limit value (Figure 3). However, it is expected that also in cities where the urban background concentration is below the limit value, limit values are exceeded at hot spots, in particular in locations with high density of traffic.

Enforcement of current EU legislation (Large Combustion Plant and IPPC Directive, Auto-Oil programme, the NEC directive) and CLRTAP protocols have resulted in a reduction of nitrogen oxides (NOx) emissions. Until now this reduction has not been reflected in the annual means observed at the urban background stations. Figure 4 showns that a large fraction of the sites are in exceedance.

Peak nitrogen dioxide levels occur often in busy streets in cities where road traffic is the main source. Since the introduction of catalytic converters at the end of the 1980s, their growing penetration in the car fleet and other measures have contributed to reducing emissions (-25% since 1980 in the EU-15). The result has been a downward trend in the number of exceedances of the short-term limit value. Peak levels depend on meteorological conditions; year-to-year fluctuations are 10 to 20 % or more even if emissions are constant.

In total 24 countries (22 EEA member countries and 2 collaborating non-member countries) have submitted information on nitrogen dioxide concentrations in urban areas to the air quality database AirBase. However, the majority of information on nitrogen dioxide concentrations is limited to the EU-15 countries. The limit value tends to be less widely exceeded in the Central and Eastern European countries.

Ozone (O3)

Although reductions in emissions of ozone precursors appear to have led to lower peak concentrations of ozone in the troposphere, the current target level is frequently exceeded for a substantial part of the urban population of the EEA-31. Figure 5 shows estimates for 2001, indicating that only 9% of the urban population experienced no exceedance of the 120 microgramme O3/m3 level, while about 30% of the urban population was exposed to concentrations above the 120 microgramme O3/m3 level during more than 25 days. The target level was exceeded over a wide area and by a large margin.

Several studies have shown that ozone peak values (given as 98-percentiles) have tended to decrease over the past 5-10 years. However, data available from AirBase for a consistent set of stations over the period 1996-2001 shows hardly any variation for the 26th highest maximum daily 8-hour mean. Figure 6 shows this 26th highest value; if it drops below 120 microgramme O3/m3, there is compliance with the target value. Furthermore, the annual mean ozone concentrations have increased, which is in agreement with previous studies. The ozone effects induced by short term exposure to high concentrations might therefore be reduced. However, there is some evidence of average chronic damage to the human lung from prolonged ozone exposure. With increasing levels, these potential effects will increase as well.

The reductions in ozone precursor emissions that should result from enforcement of the NECD and the CLRTAP Protocols are unlikely to reduce ozone concentrations to below the current target value and long-term objective over the whole of the EEA area. In north-west Europe about 25 exceedance days of the 120 microgramme O3/m3 limit are still expected in 2010.

Sulpher dioxide (SO2)

Sulphur in coal, oil and mineral ores is the main source of sulphur dioxide in the atmosphere. Up to 1960s, coal and oil combustion in large and small sources was the typical situation in many European cities, resulting in very high sulphur dioxide and PM concentrations. Since then, the combustion of sulphur-containing fuels have largely been removed from urban and other populated areas, first in western Europe and now also increasingly in most central and eastern European countries. Large point sources (power plants and industries), remain the predominate source of sulphur emissions. These sources, usually with high stacks, are most often located away from population centres.

As a result of the important reductions in sulphur dioxide emissions achieved in the last decades, the fraction of the urban population exposed to concentrations above the EU limit value has been reduced to less than 1% (Figure 7). The reduction in sulphur dioxide peak concentrations is more clearly seen in the trend of the 4th highest daily sulphur dioxide concentration on each urban station in the period 1996-2002 (Figure 8). Compliance with the limit value for the daily mean is assured when the 4th highest concentration is below 125 microgramme SO2/m3. A further decline in concentrations is expected in the coming years. However, peak concentrations above EU limit values still occur, especially close to sources and in cities. Peak levels strongly depend on meteorological conditions; year-to-year fluctuations are 10-20 % or more even for constant emissions.

Several factors have contributed to the decrease in sulphur dioxide concentrations. The first (1985) and the second (1994) sulphur protocol under the UN-ECE Convention on LRTAP, together with EC limit values set in the previous Air Quality Directive (89/427/EEC amending 80/779/EEC) have resulted in major European emission reductions and correspondingly decreasing ambient concentrations. Political changes in the beginning of 90's in the central and eastern European countries connected with economic restructuring, decline of heavy industry and adoption of abatement measures on large point sources has contributed to decreasing winter smog episodes in central and western European countries. Measures such as the Large Combustion Plants Directive, the IPPC Directive, Directives regulating emissions from transport, the National Emission Ceilings Directive, and the reductions agreed under CLRTAP are expected to further reduce sulphur dioxide levels. Programmes for the reduction of sulphur emission from ships are also underway.

For 24 of the EEA-31 countries and three other non-EEA countries information on sulphur dioxide concentrations in urban areas is available in the air quality database AirBase (Buijsman et al., 2004). However, the majority of the information on sulphur dioxide concentrations results from stations in EU-15 countries. The limit values tend to be more widely exceeded in the Central and Eastern European countries.

Data sources

Justification for indicator selection

This indicator of the exposure of urban populations to air pollution focuses on sulphur dioxide, particulate matter (PM), nitrogen oxides and ground-level ozone. Sulphur dioxide (SO2) is directly toxic to humans, its main action being on the respiratory functions. Indirectly, it can affect human health as it is converted to sulphuric acid and sulphate in the form of fine particulate matter.

Epidemiological studies have reported statistical significant associations between short-term, and especially long-term exposure to increased ambient PM concentrations and increased morbidity and (premature) mortality. PM levels that may be relevant to human health are commonly expressed in terms of PM10 meaning particulate matter which passes through a size-selective inlet with a 50 % efficiency cut-off at 10 mg aerodynamic diameter. Health effect associations for the PM2.5 fraction are even more clearly evident. Although the body of evidence concerning the health effects of PM is increasing rapidly, it is not yet possible to identify a concentration threshold below which health effects are not detectable. There is therefore no recommended WHO Air Quality Guideline for PM.

PM10 in the atmosphere can result from direct emissions (primary PM10) or emissions of particulate precursors (nitrogen oxides, sulphur dioxide, ammonia and organic compounds) which are partly transformed into particles by chemical reactions in the atmosphere (secondary PM10).

Short-term exposure to nitrogen dioxide may result in airway and lung damage, decline in lung function, and increased responsiveness to allergens following acute exposure. Toxicology studies show that long-term exposure to nitrogen dioxide can induce irreversible changes in lung structure and function.

Exposure to high ozone concentration for periods of a few days can have adverse health effects, in particular inflammatory responses and reduction in lung function. Exposure to moderate ozone concentrations for longer periods may lead to a reduction in lung function in young children.

Scientific references:

No rationale references
available

Policy context and targets

Context description

This indicator is relevant information for the Clean Air for Europe (CAFE) programme.

A combined ozone and acidification abatement strategy has been developed by the Commission, resulting in a new Ozone Daughter Directive (2002/3/EC) and a National Emission Ceiling Directive (2001/81/EC). In this legislation, target values for ozone levels and for precursor emissions have been set.

For the protection of human health in the adopted Daughter Directive for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 1999/30/EC).

Targets

EU limit values on concentrations of sulphur dioxide in ambient air

Two limit values have been set for the protection of human health. Both limit values have to be met by 1 January 2005.

a limit value of 125 mg SO2/m3 as an daily average, not to be exceeded more than three times a calendar year, has been set for the protection of human health in the adopted Daughter Directive for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 1999/30/EC, Section I of Annex I).

an hourly limit value for the protection of human health has been set at 350 mg SO2/m3; this level may not be exceeded more than 24 times a calendar year.

EU limit values on concentrations of nitrogen dioxide in ambient air

Both limit values have to be met by 1 January 2010:

In the first Daughter Directive (Council Directive 1999/30/EC, section 1 of Annex II) an annual mean limit value for nitrogen dioxide of 40 mg NO2/m3 has been set for the protection of human health.

In addition, an hourly limit value of 200 mg NO2/m3 not to be exceeded more than 18 times a calendar year has been set.

EU limit values on concentrations of PM10 in ambient air

Both limit values should be met by 1 January 2005.

a limit value for PM10 of 50 mg/m3 (24 hour average, i.e. daily), not to be exceeded more than 35 times a calendar year is set for the protection of human health by the first Daughter Directive for sulphur dioxide, oxides of nitrogen, particulate matter and lead in ambient air (Council Directive 1999/30/EC, Annex III)

an additional limit value of 40 mg/m3 as annual average has also been set.

EU target values on concentrations of ozone in ambient air

A combined ozone and acidification abatement strategy has been developed by the Commission, resulting in a new Ozone Daughter Directive (2002/3/EC) and a National Emission Ceiling Directive (2001/81/EC). In this legislation, target values for ozone levels and for precursor emissions have been set.

The Ozone Daughter Directive sets a target value for the protection of human health of 120 mg O3/m3 as maximum daily 8 hour mean, not to be exceeded more than 25 days per calendar year, averaged over three years. This target should be met in 2010 (short term objective).

The Ozone Daughter Directive has also set a long-term objective of 120 mg O3/m3 as a maximum daily 8 hour mean within a calendar year.

Directive 2001/81/EC, on nation al emissions ceilings (NECD) for certain atmospheric pollutants. Emission reduction targets for the new EU10 Member States have been specified in the Treaty of Accession to the European Union 2003 [The Treaty of Accession 2003 of the Czech Republic, Estonia, Cyprus, Latvia, Lithuania, Hungary, Malta, Poland, Slovenia and Slovakia. AA2003/ACT/Annex II/en 2072] in order that they can comply with the NECD.

Directive 2002/3/ EC of the European Parliament and of the Council of 12 February 2002 relating to ozone in ambient air

Methodology

Methodology for indicator calculation

Sulphur dioxide (SO2)

For each urban station, the number of days with a daily averaged concentration in excess of the limit value (125 mg SO2/m3 as a daily mean) is calculated from the available hourly or daily values. Only time series with a data capture of at least 75 % per calendar year are used (that is with more than 274 valid daily values per calendar year). The selected urban stations include station types "urban background" and "sub-urban background". The number of exceedance days per city is obtained by averaging the results of all "urban" and "sub-urban background" stations.

Particulate matter (PM10)

For each urban station the number of days with a daily mean concentration in excess of the limit value of 50 mg/m3 is calculated from the available hourly or daily values. The selected urban stations include station types "urban background" and "sub-urban background". Only time series with a data capture of at least 75% per calendar year are used (that is with more than 274 valid daily values per calendar year). The number of exceedance days per city, is obtained by averaging the results of all "urban" stations.

Nitrogen dioxide (NO2)

The annual mean concentration in a city is calculated as the average of the annual mean value measured at all "urban background" and "sub-urban background" stations. Only time series with a data capture of at least 75% are used (that is with more than 274 valid daily values per calendar year).

Ozone (O3)

The number of exceedance days is calculated for each "urban background" and "sub-urban background" stations. A city average number of exceedance days is obtained by averaging over all available "urban background" and "sub-urban background" stations. Only time series with a data capture of at least 75% are used (that is with more than 274 valid daily values per calendar year).

Methodology for gap filling

No gap-filling is applied for this indicator.

Methodology references

No methodology references available.

Uncertainties

Methodology uncertainty

The air quality data is officially submitted. It is assumed that data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. The data is generally not representative for the total urban population in a country. Locally, the indicator is subject to year-to-year variations due to meteorological variability.

Data sets uncertainty

SO2

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Reliability, accuracy, robustness, uncertainty (at data level): The number of available data series varies considerably from year to year and is for the first part of the 1990s insufficient. The data is generally not representative for the total urban population in a country. Availability of data before 1990 is too low to include in the indicator; data for non EU Member States is largely missing before 1995. Locally, the indicator is subject to large year-to-year variations due to meteorological variability. When averaging over EEA member countries this meteorologically induced variation decreases in importance provided spatial data coverage is sufficient. Due to deficiencies in information on station characteristics, the selection of urban sites (i.e. of the type "urban background" and "sub-urban background") might not always result in a representative selection of polluted zones. As a consequence, the indicator may be biased (see at 6).The representativeness of the selection is different for different cities which reduces the comparability between cities. It is not possible at this stage to select a sufficiently large set of stations covering the entire time period since the stations with available data change from year to year.

PM10

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the national data supplier has validated the air quality data. Station characteristics and representativeness is often insufficiently documented. Geographical coverage and data availability needs improvement; as the majority of the stations is located in EU-15 Member States, the indicator will underexpose the situation in Accession Countries. Data has been considered both from monitoring with the reference method (gravimetry) and with other methods. It is not documented whether countries have applied correction factors for non-reference methods, and if so, which factors have been applied. Uncertainties associated with this lack of knowledge may be several tens of percents.

Reliability, accuracy, robustness, and uncertainty (at data level): The number of available data series varies considerably from year-to-year and is insufficient for the period before 1997. The data is generally not representative for the total urban population in a country. Locally, the indicator is subject to year-to-year variations due to meteorological variability. When averaging over EEA-32 this meteorologically induced variation decreases in importance provided spatial data coverage is sufficient. Due to deficiencies in information on station characteristics, the selection of urban (type "urban background" and "sub-urban background") sites might not always result in a representative selection of polluted areas. The indicator may be biased due to insufficient representative coverage of the pollution situation. The representativeness of the selection is likely to be different for different cities which reduces comparability.

NO2

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Reliability, accuracy, robustness, uncertainty (at data level): The number of available data series varies considerably from year-to-year and is for the first part of the 1990s insufficient. The data is generally not representative for the total urban population in a country. Availability of data before 1990 is too low to include in the indicator; data for non EU Member States is largely missing before 1995. When averaging over EEA-32 this meteorologically induced variation decreases in importance provided spatial data coverage is sufficient. Due to deficiencies in information on station characteristics, the selection of urban sites might not always result in a representative selection of polluted zones. As a consequence, the indicator may be biased. The representativeness of the selection is different for different cities which reduces the comparability between cities. It is not possible in this stage to select a sufficiently large set of stations covering the entire time period since the stations with available data change from year to year.

O3

Strength and weakness (at data level): The air quality data is officially submitted to the European Commission under the Exchange of Information Decision. It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented. Data coverage in non EEA-32 member countries needs improvement; data availability over the period 1980-1995 needs improvement.

Reliability, accuracy, robustness, uncertainty (at data level): The number of available data series varies considerably from year to year and is for the first part of the 1990s insufficient. Yearly changes in indicator value may result from changes in monitoring density and/or selected cities which will influence the total monitored population. The indicator is subject to year-to-year fluctuations as it represents episodic conditions, and these depend on particular meteorological situations, the occurrence of which varies from year to year.